The production of butanol by solvent-producing strains of Clostridium spp. was one of the most important biotechnological developments in the first half of the 20th Century. Butanol is currently used as a chemical in the production of lacquers, plasticizers, coatings, detergents, and brake fluids. Furthermore, it is useful as a chemical substrate in the plastics industry and as a fuel additive. There is a growing interest in enhancing butanol production via butanol fermentation in bacteria. However, end-product inhibition is often a barrier to efficient productivity in many industrial fermentation processes. This toxicity results in lower than ideal final titers of butanol.
Attempts have been made to adapt fermenting bacteria to growth-limiting conditions. Toxic solvents induce the synthesis of heat shock proteins. The overexpression of heat shock proteins GroESL in Clostridium acetobutylicum results in less inhibition of clostridial growth by butanol challenge and increased final solvent titers. However, the cells are sensitive to low concentrations of butanol.
Efforts to obtain mutants that can tolerate and produce higher concentrations of butanol have been met with limited success. Butanol toxicity may have multiple effects on the cell. While there have been a few butanol-tolerant mutants to produce higher concentrations of solvent than their respective parent strains, none have been able to produce desired solvent levels.
There remains a need for the development of strains that have enhanced butanol end product tolerance and therefore can produce industrially viable concentrations of butanol.